Smallmatrix

<..equations of amsmath.sty..>+
                                     \catcode‘\#=13 \catcode‘\!=6
 \def\reg:smallmatrix{%
   \vcenter\bgroup \Let@\restore@math@cr\default@tag
   <.ialign amsmath smallmatrix.>}
                                     \catcode‘\#=6 \catcode‘\!=12
 -_-_-

<..ialign amsmath smallmatrix..>
 \SaveMkHalignConf:g{smallmatrix}%\HRestore\noalign
 \MkHalign#{$\m@th\scriptstyle#$&&%
            $\m@th\scriptstyle#$}%
 -_-_-

<..equations of amsmath.sty..>+
 \def\:tempc{\crcr\EndMkHalign
     \RecallMkHalignConfig \egroup\b:smallmatrix}
 \HLet\endsmallmatrix=\:tempc
 \def\:temp{\pic:MkHalign{smallmatrix}}
 \HLet\smallmatrix=\:temp
 \NewConfigure{smallmatrix}{6}
 -_-_-